Field sequential color ferroelectric liquid crystal display cell

ABSTRACT

An electrically suppressed helix (ESH) ferroelectric liquid crystal (FLC) display cell with fast response includes: a liquid crystal layer, disposed between two transparent substrates, wherein helix pitch of chiral smectic liquid crystals of the liquid crystal layer is less than the thickness of the liquid crystal layer; at least one polarizer; and a voltage source, configured to apply electrical driving voltage pulses to electrodes of the display cell with amplitude greater than a critical voltage for helix unwinding of the chiral smectic liquid crystals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of copending U.S.patent application Ser. No. 14/070,149, filed on Nov. 1, 2013, whichclaims the benefit of U.S. Provisional Patent Application No.61/796,034, filed on Nov. 1, 2012. This patent application also claimsthe benefit of U.S. Provisional Patent Application No. 62/177,243, filedon Mar. 10, 2015. All of the foregoing applications are incorporated byreference herein in their entireties.

FIELD

The present invention relates to a liquid crystal (LC) display. Moreparticularly, the invention relates to a field sequential color (FSC)display based on a ferroelectric liquid crystal display (FLCD) cell withfast response having alignment quality comparable to nematic LCs, theFLCD cell comprising a chiral smectic liquid crystal whose helix pitchis less than the thickness of LC layer.

The present invention further relates to a display cell based on aferroelectric liquid crystal display (FLCD) cell with fast responsehaving alignment quality comparable to nematic LCs, the FLCD cellcomprising FLCs whose helix pitch is less than the thickness of LClayer.

Applications of LC display cells having fast response, high resolution,and high contract include, for example, fast-response photonics devices(e.g., modulators, filters, attenuators) and high-resolution displays(e.g., pico-projector, 3D display, micro-display, HDTV).

BACKGROUND

Conventional displays are designed on basis of spatially “simultaneousadditive color mixing process.” FSC displays, on the other hand, inwhich color displaying can be carried out with one pixel, use a“successive additive color mixing process” by a temporally-dividedbacklight system. FSCDs offer several fundamental advantages overconventional transmissive and emissive displays. The absence ofsub-pixels and color filters give high transmission, large apertureratio, and the possibility of at least three times higher pixel densityas well as three times less power consumption. Furthermore, the primarychromaticity is determined solely by the light sources, which enableswider gamut. However, an inherent problem of FSCDs is the presence ofsaccadic color break-up artifacts. These artifacts may be eliminatedonly by increasing the frame rate, which requires LCs with fast responsetime.

Due to fundamental working principle of FSCDs, conventional nematic LCscannot satisfy the high frequency requirement to avoid color break up.However, a number of other LC-based architectures and electro-opticalmodes have been proposed for FSCDs to attempt to improve the responsetime for LCs.

One approach uses the flexoelectric effect of short pitch cholestericLCs shows a response time of ˜200 μs. This technology, however, hasseveral material issues and a very complicated fabrication procedure.

In some alternate approaches, polymer-stabilized blue phase liquidcrystal and cholesteric liquid crystal have been proposed with very fastresponse time (around 1 ms). Drawbacks which limit these technologiesare the very high requirement of driving voltage at the electric fieldof E=20 V/μm and several material issues.

FLCs, because of their fast response times, are another possibility forFSCDs. One approach is a polymer stabilized FLC to enable monostableV-shape switching (hereinafter abbreviated PSV-FLCD). Another approachis a photoaligned fast FLC display using deformed helix ferroelectric(hereinafter abbreviated DHF) mode LC used for FSCDs, for example, asdescribed in U.S. patent application Ser. No. 13/110,680 (published asU.S. Publication No. 2011/0285928), which is incorporated herein byreference in its entirety. The electronic driving scheme for this DHFFLC includes amplitude modulation, which may increase the fabricationexpense.

Recently, in-plane switching (IPS), Advanced Super Dimension Switching(ADS), and fringe field switching (FFS) have been used in high-end LCDapplications because they provide wide view angle and high resolution.However, such conventional IPS, ADS and FFS devices suffer from severedrawbacks in terms of image-sticking due to residual DC (RDC) of thealignment layer, as well as non-uniformity and loss of lighttransmittance at the edge of the pixels due to non-uniformity liquidcrystal alignment. Image flickering is also an issue with respect to FFSdisplays, and complex fabrication and manufacturing costs are additionaldrawbacks as well.

While FLCs, due to their in-plane switching behavior, provide theadvantages of fast switching speed and lower power consumption alongwith simpler and cheaper fabrication. However, due to certainlimitations of FLCs (e.g., the geometrical, optical and mechanicaldefects associated therewith), FLCs have not conventionally been adoptedfor high-end LCD applications.

SUMMARY

In an exemplary embodiment, an electrically suppressed helix (ESH)ferroelectric liquid crystal (FLC) display cell with fast responseincludes: a liquid crystal layer, disposed between two transparentsubstrates, wherein helix pitch of chiral smectic liquid crystals of theliquid crystal layer is less than the thickness of the liquid crystallayer; at least one polarizer; and a voltage source, configured to applyelectrical driving voltage pulses to electrodes of the display cell withamplitude greater than a critical voltage for helix unwinding of thechiral smectic liquid crystals.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in even greater detail below based onthe exemplary figures. The invention is not limited to the exemplaryembodiments. All features described and/or illustrated herein can beused alone or combined in different combinations in embodiments of theinvention. The features and advantages of various embodiments of theinvention will become apparent by reading the following detaileddescription with reference to the attached drawings which illustrate thefollowing:

FIG. 1A is a diagram illustrating the components of an FSC FLC displaycell in an exemplary embodiment;

FIG. 1B is a diagram illustrating the components of an FSC FLC displaycell in another exemplary embodiment;

FIG. 2 is a diagram illustrating liquid crystal structure in anexemplary embodiment;

FIG. 3 is a graph illustrating an electro-optical response of an ESH FLCdisplay cell in an exemplary embodiment;

FIG. 4 contains graphs illustrating a driving scheme for an ESH FLC FSCdisplay cell in an exemplary embodiment;

FIG. 5 contains images showing achieved colors (in black & white) havingdifferent gray levels using an ESH FLC FSC display cell in an exemplaryembodiment;

FIG. 6 is a graph illustrating display colors achieved by an ESH FLC FSCdisplay cell in an exemplary embodiment with respect to a CIE 1931 colorspace;

FIG. 7 is a graph illustrating contrast ratio dependency on drivingvoltage frequency of an ESH FLC FSC display cell in an exemplaryembodiment;

FIG. 8 is a diagram illustrating angular dependence of the transmittanceof an ESH FLC FSC display cell in an exemplary embodiment;

FIG. 9 is a graph illustrating an electro-optical response of an ESH FLCdisplay cell in an exemplary embodiment;

FIG. 10 is a plot illustrating electro-optical characteristics of anexemplary ESH FLC display cell;

FIG. 11 is a grayscale reproduction of an optical microphotographdepicting an ESH FLC display cell having two domains in the absence ofthe electric field; and

FIG. 12 is a grayscale reproduction of optical microphotographs of anESH FLC display cell with an applied electric field greater than thecritical field for helix unwinding showing bright (left image) and dark(right image) states at +1V and −1V respectively.

DETAILED DESCRIPTION FSC FLC Display Cells

Certain embodiments of the invention relate to a field sequential color(FSC) display based on an electrically suppressed helix (ESH)ferroelectric liquid crystal (FLC) display cell structure which exhibitsfast response (e.g., less than 10 μs at an applied electric field of6.67 V/μm), wide viewing angle, high contrast ratio (e.g., 10000:1 at3.5 volts/μm) and a large color triangle (e.g., more than 130% of thearea of a standard NTSC (National Television System Committee) colortriangle with respect to CIE 1931 color space at 3.5 volts/μm).

Further, in an exemplary embodiment, an FLC FSCD was able to achieve aframe frequency of 240 Hz, as well as 24-bit color (by changing theresidual light of the cell to generate 8-bit gray levels in each ofthree subframes). Additionally, the FSC display exhibited saturatedelectro-optical modulation up to a frequency of 5 kHz under an appliedelectric field of 5 volts/μm.

ESH mode is another electro-optical mode of an FLC cell. An ESH FLCcell, in an embodiment of the invention, comprises FLCs with helix pitchless than the thickness of the LC layer, which thereby provides adefect-free layer of FLCs under an applied electric field higher thanthe critical electric field threshold for helix unwinding. The FLC layeris configured such that the helix elastic energy is slightly higher thanthe effective anchoring energy of the alignment layer (e.g., about 1 to3 times the anchoring energy), allowing for the ESH electro-optical modeto be achieved in an FLC cell. The ESH FLC cell has an extremely fastresponse, and has alignment quality on the same level as nematic LCs.The ESH FLC cell is placed between two polarizers, and is connected to asource of electrical driving voltage that provides the applied electricfield via electrodes. The ESH FLC cell provides high contrast, smallresponse time at very high frequency, and very low power consumption.

There are several differences between an ESH FLC cell and a DHF FLCcell. An FLC cell to be operated in DHF mode requires a tilt angle closeto 45° and spontaneous polarization of more than 150 nC/cm², whereas foran ESH FLC cell the tilt angle should be around 22.5° and thespontaneous polarization should be more than around 50 nC/cm².Furthermore, the helix of FLCs in an ESH FLC cell should be sufficientlylarge but while being smaller than the cell gap to provide balancebetween elastic and anchoring energy of the system (e.g., 2 to 5 timessmaller than the cell gap). As noted above, for an ESH FLC cell, theelastic energy of the helix must be comparable to but larger than theanchoring energy of the alignment (e.g., about 1 to 3 times theanchoring energy).

Additionally, the driving scheme for an ESH FLC cell is entirelydifferent from a DHF FLC cell. The ESH FLC cell is a mono stable FLCcell having only two states (bright or dark) and thus uses a pulse widthmodulation driving scheme to generate gray scales (an amplitudemodulation scheme would not be able to generate gray scales with respectto an ESH FLC cell), whereas a DHF FLC cell uses an amplitude modulationscheme in order to generate different brightness to achieve grayscale.

An exemplary overall architecture for an FSC display including an FLCcell and light emitting diodes (LEDs) to illuminate pixels in atime-sequential manner is depicted in FIG. 1A. The FSC display includespolarizers 104 and 106, substrates 103A and 103B, an ITO conductivelayer 102, alignment layers 101A and 101B, a thin film transistor array105 for providing a driving voltage, light emitting diode (LED)backlighting 108, and FLC layer 107.

An alternative exemplary overall architecture for an FSC displayincluding a reflective FLC cell is depicted in FIG. 1B. The reflectiveFLC cell includes a polarizer 904, substrates 903A and 903B, an ITOconductive layer 902, alignment layers 901A and 901B, a thin filmtransistor array 905 for providing a driving voltage, a reflectivemirror layer 906, and FLC layer 907. It will be appreciated that in thisexemplary overall architecture, LED backlighting is not used.

It will be appreciated that in FIGS. 1A and 1B, the substrates maycomprise glass and/or plastic material, and that the alignment layersmay be prepared by photoalignment, rubbing, and/or oblique evaporation(and with precise control of the corresponding anchoring energy).

Exemplary embodiments of the invention will be discussed with furtherdetail with respect to FIGS. 2-7. FIG. 2 depicts a diagram thatillustrates a chiral liquid crystal layer representing a ferroelectricliquid crystal of chiral smectic C* phase whose helical structure has apitch P₀ smaller than a gap d between the first and the secondsubstrates of an FLC display cell. Given an FLC layer thickness dgreater than helical pitch P₀, and with an applied voltage V that isgreater than the critical voltage for helix unwinding (hereinafterabbreviated V_(c))—i.e. V>V_(c)—the FLC display cell is in the ESHelectro-optical mode.

Element 1 corresponds to substrates, which are transparent with respectto visible light. Element 2 corresponds to conductive layers, which aretransparent with respect to visible light and covered by an aligninglayer. Element 3 corresponds to smectic layers, which are perpendicularto the substrates. Element 4 corresponds to a source of driving voltageapplied to the conductive layers 2.

β corresponds to an angle between polarizer plane and the helix axes inthe absence of an applied voltage. D corresponds to light beam aperture,which is considerably larger (e.g., at least approximately 10-20 timeslarger) than the helix pitch. An XYZ coordinate system is also depictedfor reference purposes. The Z-axis is aligned along the helix axes andthe principle optical axes of the liquid crystal layer. The X-axis isperpendicular to the substrates, and the Y-axis is parallel to thesubstrates.

FIG. 3 depicts a graph illustrating the electro-optical response of anESH FLC display cell in an exemplary embodiment. The top waveformcorresponds to an applied voltage (left-side axis) over time. The bottomwaveform corresponds to electro-optical response of the ESH FLC displaycell (right-side axis) over time. The operating conditions to obtainthis waveform included: temperature (T)=22° C., wavelength (λ)=0.63 m,and operational frequency (f) of 3 kHz. As can be seen from FIG. 3, ESHelectro-optical mode provides for very fast electro-optical responsetime and allows for high frequency electro-optical modulation.

Additionally, an embodiment of the ESH FLC display cell was able tomanifest electro-optical modulation with saturated bright and darkstates up to the applied voltage frequency of 5 kHz at the electricfield of 5 V/μm. With this high operation frequency of 5 kHz, the framerate of 240 Hz for field sequential color display can be achieved. And,by using light emitting diodes (LEDs) to illuminate pixels sequentiallyin time pursuant to pulse-width modulation, the residual light of thecell can be adjusted to generate different colors and levels ofgrayscale.

FIG. 4 depicts graphs illustrating a driving scheme for an ESH FLC FSCdisplay cell. The top three graphs are voltage waveforms applied toblue, green and red LEDs of the display cell, respectively. Based on theapplication of these voltage waveforms, the three color LEDs aresequentially turned ON and OFF over time. The fourth graph (at thebottom) corresponds to a voltage waveform applied to the ESH FLC cell ofthe ESH FLC FSC display cell. The dashed square represents coupling ofthe electro-optical response of the ESHFLC cell with different LEDs'bright states (i.e., during the time period encompassed by the dashedbox, the FLC cell is being driven with the red LED off, the blue LEDoff, and the green LED on).

Thus, as shown by FIG. 4 which represents an example of an “on” frame,24-bit color is achievable by an ESH FLC FSC display cell in anembodiment (based on RGB subframes with 8-bit gray levels, using a pulsewidth modulation driving scheme where residual light is varied based onvariation of the bright time with respect to each subframe to achieveintermediate colors and shades). Accordingly, a total of 2²⁴ colors canbe achieved (over 16 million).

FIG. 5 depicts a grayscale reproduction of a photograph demonstratingsome of the achieved colors with different gray levels. A colorreproduction of this image can be found in A. Srivastava et al., “FullColor Field Sequential Color Display Based on Electrically SuppressedHelix FLC”, Presentation at LCD-4, EuroDisplay 2013, which isincorporated herein by reference in its entirety.

FIG. 6 is a graph depicting observed ESH FLC FSC display colors asrepresented with respect to the CIE 1931 color space. The areaencompassed by the color triangle corresponding to an ESH FLC FSCdisplay in an embodiment of the invention, which was achieved with anapplied electric field of less than 3.5 volts/μm (i.e., 3.33 volts/μm),is about 130% of the area encompassed by the standard NTSC colortriangle. It will be appreciated that the large color triangle achievedin this embodiment is based solely on the LEDs and the efficiency of theLEDs, as no color filters are used. Additionally, the ESH FLC FSCdisplay achieves a wide viewing angle (i.e., about 85 degrees from thenormal position for each side) due to the utilization of in-planeswitching.

FIG. 7 depicts a graph illustrating dependency of the contrast ratio ofan ESH FLC FSC display cell on driving voltage frequency at an appliedelectric field of 1.5 V/μm, 3 V/μm and 5 V/μm. As depicted in FIG. 7,the ESH FLC FSC display cell with d>P₀ provides very high contrast ratioup to very high operating voltage frequencies. For example, the contrastachievable with the ESHLC FSC display cell in an embodiment is more than10000:1 up to a frequency of 5 kHz at an operating voltage of 5 V/μm.

FIG. 8 is a diagram illustrating the angular dependence of thetransmittance of an ESH FLC FSC display cell. FIG. 8 shows that wideviewing angle is achieved (i.e., about 85 degrees from the normalposition for each side). Referring to the “normal position” as beingdirectly in front of the display cell, the transmittance at about 70°from the normal position was demonstrated in an embodiment to be about60% of its maximum value at the normal position.

Other FLC Display Cell

Other exemplary embodiments of the invention relate to displays(including non-FSC displays) based on an electrically suppressed helix(ESH) ferroelectric liquid crystal (FLC) display cell structure whichexhibits fast response (e.g., less than 10 μs at an applied electricfield of 6.67 V/μm), wide viewing angle, and high contrast ratio (e.g.,10000:1 at 3.5 volts/μm).

In particular, by using nano-scale photoalignment (i.e., applying aphotosensitive alignment layer having a thickness that is in thenanometer range) together with ESH FLC technology, LCD displays havingfast electro-optical response, high contrast ratio, wide viewing angle,and relatively low power consumption can be achieved. In exemplaryembodiments, a frame frequency of 240 Hz has been demonstrated for anESH FLC display with more than 8-bit gray levels being generated.Further, the ESH FLC display is characterized by very high opticalcontrast, small electro-optical response time and saturatedelectro-optical modulation (at frequencies up to 5 kHz with an appliedelectric field of 5 V/μm). The ESH FLC display further achieves highcontrast (e.g., 10000:1) with wide viewing angle with an appliedelectric field of 3.5 V/μm.

As discussed above with respect to FIG. 2, an exemplary ESH FLC displaycell includes a helical structure of chiral smectic C* phase layer whosethickness d is bigger than the helix pitch p₀. The display cell includessubstrates, transparent for the visible light (element 1); conductivelayers, transparent for the visible light and covered with any aligninglayer (element 2); smectic layers, which are perpendicular to thesubstrates (element 3), and a source of driving voltage (element 4). βis an angle between polarizer plane and the helix axes at the absence ofthe applied voltage, and D is a light beam aperture, which isconsiderably bigger than the helix pitch. The Z-axis is aligned alongthe helix axes and the principle optical axes of the liquid crystallayer, the X-axis is perpendicular to the substrates, and the Y-axis isparallel to the substrates.

The chiral liquid crystal layer represents a ferroelectric liquidcrystal of chiral smectic C* phase whose helical structure has a pitchP₀ smaller than a gap d between the first and the second substrates ofthe cell. For the FLC layer thickness d greater than helical pitch P₀and the applied voltage V is greater than the critical voltage for thehelix unwinding (hereinafter abbreviated V_(e))—i.e. V>V_(c)—ESHelectro-optical mode exists. The ESH electro-optical mode manifests verysmall electro-optical response time and high frequency electro-opticalmodulation, and the cell manifests electro-optical modulation withsaturated bright and dark states up to the applied voltage frequency of5 kHz at the electric field of 5V/μm. This is depicted in FIG. 9, whichshows the electro-optical response of an exemplary ESH FLC display cell,where the top portion of FIG. 9 is the applied voltage and the bottomportion of FIG. 9 represents electro-optical response of the ESH FLCdisplay cell at temperature (T)=22° C., wavelength (λ)=0.63 μm andoperational frequency (f) of 1 kHz.

The exemplary ESH FLC display cell is able to generate more than 8 bitgray levels using a driving scheme based on multiple pulse modulationsor pulse width modulation. This has been demonstrated with variation ofthe residual light by varying the bright time of the display cell. Theintermediate or different gray scales can be generated by simplevariation in the bright time of the ESH FLC display cell for differentpurposes.

The response times of the ESH FLC display cell, for both the switchingON and switching OFF time, are illustrated in FIG. 10 as a function ofapplied voltages. Specifically, FIG. 10 illustrates the electro-opticalcharacteristics of an exemplary ESH FLC display cell. The bottom solidcircles show the response time as a function of applied drivingvoltages. The solid circles on the top show optical contrast as afunction of applied frame frequencies at a driving voltage of 2 V/μm.

In the example illustrated in FIG. 10, the response time is 30 μs at theapplied voltage magnitude of 10 V. It can also be seen that the responsetime first increases with the applied voltage and shows a maximum, whichcorresponds to the critical field of helix unwinding. At voltages abovethe maximum, it decreases at higher electric fields.

As discussed above, FIG. 7 illustrates the dependency of contrast ratioson driving voltage frequencies with respect to an exemplary ESH FLCdisplay cell. An ESH FLC cell with d>P₀ provides very high contrastratio up to very high operating voltage frequency. The contrast for anexemplary ESH FLC display cell is more than 10000:1 up to frequencies of5 kHz at an operating voltage of 5 V/μm. Further, the exemplary ESH FLCdisplay cell shows high contrast with optically saturated bright anddark states. The optically saturated states, as depicted in FIG. 7, areobserved until 1 kHz, 3 kHz and 5 k-Hz at electric fields of 1.5 V, 3 Vand 5 V, respectively. The frequency range for the saturated opticalstates can also be increased by applying higher magnitude for theelectric field. Thus, the ESH FLC display cell is characterized by thewide viewing angle, fast response time, high contrast and low drivingvoltages.

Additionally, as discussed above, FIG. 8 illustrates the luminanceangular dependence of the transmittance. FIG. 8 shows that an ESH FLCdisplay achieves a wide viewing angle and transmittance at 70° from thenormal position, while the transmittance is 60% of its maximum value atthe normal position.

In an exemplary embodiment, a electrically suppressed helix (ESH)ferroelectric liquid crystal (FLC) display cell with fast responseincludes: a liquid crystal layer, disposed between two transparentsubstrates, wherein helix pitch of chiral smectic liquid crystals of theliquid crystal layer is less than the thickness of the liquid crystallayer; at least one polarizer; and a voltage source, configured to applyelectrical driving voltage pulses to electrodes of the display cell withamplitude greater than a critical voltage for helix unwinding of thechiral smectic liquid crystals.

In a further exemplary embodiment, the substrates comprise transparentglass or plastic.

In a further exemplary embodiment, the substrates are each covered witha conducting layer or conducting polymer.

In a further exemplary embodiment, the ESH FLC display cell furthercomprises: an alignment layer disposed on at least one of thesubstrates, wherein the alignment layer is one of the group consistingof: a photo-alignment layer, a rubbed polyimide layer, and an alignmentlayer formed by oblique evaporation or ion beam deposition.

In a further exemplary embodiment, anchoring energy of the alignmentlayer is comparable to and not larger than elastic energy of the helixof the liquid crystal layer, providing a two-domain alignment for theliquid crystal layer. In an exemplary implementation, the anchoringenergy of the alignment layer may be half or three quarters relative tothe elastic energy of the FLCs, but it will be appreciated thatdifferent relationships may be suitable for different FLC materials.

FIG. 11 is a grayscale reproduction of an optical microphotographdepicting an ESH FLC display cell having two domains in the absence ofthe electric field. The two domains appear in the absence of theelectric field because the elastic energy of the helix is balanced bythe anchoring energy of the alignment layer.

FIG. 12 is a grayscale reproduction of optical microphotographs of anESH FLC display cell with an applied electric field greater than thecritical field for helix unwinding showing bright (left image) and dark(right image) states at +1V and −1V respectively. When the appliedelectric field is higher than the critical field of the helix unwinding,then only the bright or dark state will appear (based on the polarity ofthe applied voltage).

In a further exemplary embodiment, and as can be seen in FIGS. 11 and12, the liquid crystal layer has a steady state corresponding to atwo-domain alignment in the absence of applied voltage, wherein theprincipal optical axes of the two domains are deployed at an anglerelative to each other; and under an applied driving voltage withamplitude greater than the critical voltage for helix unwinding, one ofthe two domains is transformed into the other or vice versa based on thepolarity of the applied voltage, so as to provide a defect-free layer ofchiral smectic liquid crystal. The peak illustrated in the FIG. 10corresponds to the critical applied voltage (voltages above the criticalapplied voltage cause only a uniform state to exist).

In a further exemplary embodiment, the chiral smectic liquid crystallayer is a ferroelectric liquid crystal layer of chiral smectic C*phase.

In a further exemplary embodiment, the ESH FLC display cell comprisestwo polarizers, wherein the two polarizers are crossed.

In a further exemplary embodiment, the ESH FLC display cell isreflective and comprises only one polarizer.

In a further exemplary embodiment, the ESH FLC display cell isconfigured to manifest an electro-optical modulation with saturatedbright and dark states up to an applied voltage frequency ofapproximately 5 kHz at an electric field of approximately 5 V/μm.

In a further exemplary embodiment, the driving voltage is provided viaactive addressing, passive addressing or direct addressing of one ormore pixels corresponding to the ESH FLC display cell.

In a further exemplary embodiment, the ESH FLC display cell isconfigured to provide grayscale via pulse width modulation or multiplepulse modulation of the driving voltage.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. An electrically suppressed helix (ESH) ferroelectric liquid crystal(FLC) display cell with fast response, comprising: a liquid crystallayer, disposed between two transparent substrates, wherein helix pitchof chiral smectic liquid crystals of the liquid crystal layer is lessthan the thickness of the liquid crystal layer; at least one polarizer;and a voltage source, configured to apply electrical driving voltagepulses to electrodes of the display cell with amplitude greater than acritical voltage for helix unwinding of the chiral smectic liquidcrystals.
 2. The ESH FLC display cell according to claim 1, wherein thesubstrates comprise transparent glass or plastic.
 3. The ESH FLC displaycell according to claim 2, wherein the substrates are each covered witha conducting layer or conducting polymer.
 4. The ESH FLC display cellaccording to claim 1, further comprises: an alignment layer disposed onat least one of the substrates, wherein the alignment layer is one ofthe group consisting of: a photo-alignment layer, a rubbed polyimidelayer, and an alignment layer formed by oblique evaporation or ion beamdeposition.
 5. The ESH FLC display cell according to claim 4, whereinanchoring energy of the alignment layer is comparable to and not largerthan elastic energy of the helix of the liquid crystal layer, providinga two-domain alignment for the liquid crystal layer.
 6. The ESH FLCdisplay cell according to claim 1, wherein the liquid crystal layer hasa steady state corresponding to a two-domain alignment in the absence ofapplied voltage, wherein the principal optical axes of the two domainsare deployed at an angle relative to each other; and wherein, under anapplied driving voltage with amplitude greater than the critical voltagefor helix unwinding, one of the two domains is transformed into theother or vice versa based on the polarity of the applied voltage, so asto provide a defect-free layer of chiral smectic liquid crystal.
 7. TheESH FLC display cell according to claim 1, wherein the chiral smecticliquid crystal layer is a ferroelectric liquid crystal layer of chiralsmectic C* phase.
 8. The ESH FLC display cell according to claim 1,wherein the ESH FLC display cell comprises two polarizers, wherein thetwo polarizers are crossed.
 9. The ESH FLC display cell according toclaim 1, wherein the ESH FLC display cell is reflective and comprisesonly one polarizer.
 10. The ESH FLC display cell according to claim 1,wherein the ESH FLC display cell is configured to manifest anelectro-optical modulation with saturated bright and dark states up toan applied voltage frequency of approximately 5 kHz at an electric fieldof approximately 5 V/μm.
 11. The ESH FLC display cell according to claim1, wherein the driving voltage is provided via active addressing,passive addressing or direct addressing of one or more pixelscorresponding to the ESH FLC display cell.
 12. The ESH FLC display cellaccording to claim 1, wherein the ESH FLC display cell is configured toprovide grayscale via pulse width modulation or multiple pulsemodulation of the driving voltage.